Capsule-carrying sheets or webs

ABSTRACT

A capsule-carrying sheet or web, e.g. a sheet carrying capsules containing a colour-reactant material for use in a pressuresensitive copying system, in which one surface of the sheet or web carries a coating incorporating the capsules, together with starch particles acting as a protection for the capsules against accidental rupture and a protein binder binding the capsules and starch particles together on the surface, both the starch particles and the protein binder being derived from a common milled flour source, e.g. by agitation of an aqueous suspension of the milled flour.

United States Patent Evans Aug. 19, 1975 [54] CAPSULE-CARRYING HEETS 0R wE s 3,640,756 2 1972 Beersma et al. 117 156 x 3,697,323 I0 1972 B t l. 117 36.2 X [75] Inventor: Bria" Edward Evans Beaconsfieid 3 746 563 771973 F221; 2:21. ll7;36.8 X England 3,758,324 9/1973 Barrett 117 156 x [73] Assignee: Wiggins Teape Research &

Development Limited, London, Prinmry Exan'zirirThomas J. Herbert, Jr. England Attorney, Agent, or Firm-Burns, Doane, Swecker & M' 22 1 Flled: Oct. 6, 1972 211 App]. No.: 295,484 [57] ABSTRACT A capsule-carrying sheet or web, e.g. a sheet carrying [30] Forelgn Apphcatlon Pnonty Data capsules containing a colour-reactant material for use Oct. 18, United Kingdom in a pressure.sensitive opying ystem in one surface of the sheet or web carries a coating incorpo- US. rating the capsules, together with starch particles act- 106/130 ing as a protection for the capsules against accidental [5 Il'rt. Cl. rupture and a binder the capsules and Fleld of Search t l tarch particlestogether on the urface both the starch particles and the protein binder being derived References Clted from a common milled flour source, e.g. by agitation UNITED STATES PATENTS of an aqueous suspension of the milled flour.

2,730,457 H1956 Green et a] 117/368 3,573,085 3 1971 Hemstock.... 117/362 9 N0 Drawmgs BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to capsule-carrying sheets or webs and methods of producing such sheets or webs, and is particularly but not exculsively concerned with capsule-carrying sheets or webs for use in pressuresensitive copying systems.

2. Description of the Prior Art The art of encapsulation has in recent years achieved considerable commercial importance since encapsulation provides a method of maintaining a reactive material in an inert state by providing a non-reactive capsule wall between the reactive material and its surroundings. Encapsulation also enables the handling properties of solids to be conferred on liquids and gases.

It is known to encapsulate, for example, dyes, inks, chemical reagents, pharmaceuticals, flavourings, pesti cides, herbicides an d in fact any material which can be dissolved, suspended or otherwise constituted in or as a liquid internal phase enclosed within a capsule wall. The capsule serves to maintain the internal phase in its liquid, or some other converted form, at least until the internal phase is released by rupture, melting, dissolving or other removal of the capsule wall, or until the internal phase is caused to diffuse out through the capsule wall.

Various methods of encapsulation are well known, the most commonly used methods involving either a coacervation reaction, a precipitation reaction, 'or a polymerisation reaction.

A disadvantage of capsules produced by known methods is that they are not sufficiently inherently strong to prevent accidental rupture thereof, this being a particular disadvantage in pressure-sensitive copying systems where accidental rupture of capsules can result in undesirable marking of the copy sheet.

In order to increase the resistance of a capsulecarrying sheet or web, for use in a pressure-sensitive copying system, against accidental rupture of the capsules, it is known to coat cellulose fibres onto the sheet or web with the capsules, the cellulose fibres subsequently affording protection for the capsules against accidental rupture while still allowing rupture thereof by localised pressure from, for example, writing, typing or printing on the sheet or web.

In British Patent Specification No. 1,232,347 there is described another method of affording protection against accidental rupture of capsules in a pressuresensitive copying system, in which method the previously described cellulose fibres are replaced, at least in part, by finely divided particles of starch or starch derivatives. Starch particles said to be suitable include those produced from wheat, Indian corn, potato, sweet potato, sago, tapioca, rice, glutinous rice and glutinous corn.

British Patent Specification No. 1,232,347 teaches that the starch particles must be dispersed in a capsule coating layer carried on a sheet or web, and thus that the starch particles must not be dissolved in the capsules coating mix prior to coating thereof onto a sheet or web. In particular, the specification teaches that in order to prevent gelatinisation of the starch particles, the capsule coating mix must be at a temperature of less than 50C, preferably less'than 35C, when the starch particles are added thereto.

In known methods of producing a capsulecarrying sheet or web also carrying cellulose fibres as protection for the capsules, the capsules and cellulose fibres are coated onto a base sheet or web in admixture with a gelatinised starch solution which is to serve as a binder between the capsules and the cellulose fibre, and the base sheet or web. The sheet or web produced thus carries a coating including capsules, protection for the capsules, i.e. the cellulose fibres and a binder for the capsules and the cellulose fibres, i.e. the gelatinised starch solution.

SUMMARY According to one aspect of this invention, a capsulecarrying sheet or web comprises a base sheet or web having on a surface thereof a coating comprising capsules, derived starch particles (as herein defined) as protection for the capsules, and a derived protein binder (as herein defined) for the capsules and derived starch particles.

Throughout this specification the expressions derived starch particles and derived protein binder are used to denote particles and binder derived from a common milled flour source by suitable treatment thereof.

Flour, e.g. wheat grains, comprises starch particles bound together by protein material, the grains of flour being known as endosperm. Milling of such flour fractures the grains into the following four parts, the pro portions of the parts obtained being dependent to some extent upon the milling conditions but to a greater extent upon the hardness of the grains:

- size 0 10am size 20 40am size 0 20pm size 20pm It is known to use protein as a binder in paper making, and we have found that by suitable treatment of a milled flour is is possible to dissolve the protein therein and then use the dissolved protein as a binder to bind capsules and unmodified starch particles from the mill ed flour, to a base sheet or web.

Thus the invention enables the protection for the capsules (namely the starch particles) and the binder (namely the protein) to be obtained from a single source which is inexpensive and convenient to use.

A suitable treatment of milled flour to derive the starch particles and binder for the capsule-carrying sheet or web of this invention is agitation of an aqueous suspension of the milled flour for a time dependent upon the temperature of the suspension thereby to dissolve the protein fragments, the time varying between about 1 hour for a room-temperature suspension and 102O minutes for a suspension at C. Caustic soda can be added to the aqueous suspension to help in solubilising the protein fragments. Clearly the temperature of the suspension must not be such as to cause gelatinisation of the starch particles, and thus the upper temperature limit for the suspension is about C.

According to another aspect of this invention, a method of producing a capsule-carrying sheet or web according to this invention, comprises the steps of treating milled flour by agitation of an aqueous suspension thereof to provide derived starch particles (as herein defined) and derived protein binder (as herein defined), and coatingthe derived starch particles and derived protein binder onto a base sheet or web together with capsules.

Optimum protection for the capsules, with minimum effect on the other properties of a capsule-carrying sheet or web, is provided by starch particles of a size between about 1 /2 and 2 times the average size of the capsules and thus it is preferable to provide a majority of derived starch particles of such size. Capsules presently used in pressure-sensitive copying systems are normally within the size range 320;.tm. Thus, milled flour can be pre-treated, for example by air classification, to remove the small size range (l0um) starch particles mentioned above, prior to treatment thereof to derive the starch particles and binder for a capsulecarrying sheet or web according to this invention.

However, it has been suggested (see US. Pat. No. 3,573,085) that rigid microscopic particles be scattered among the capsules on a capsule-carrying sheet or web of a pressure-sensitive copying system, the rigid microscopic particles assisting in rupture of the capsules on application of localised pressure to the capsule-carrying sheet or web. The small size range (O-lOum) starch particles can therefore be retained, during treatment of milled flour to derive the starch particles and binder of the capsule-carrying sheet or web of this invention, to serve as rupture-assisting particles as described above.

DETAILED DESCRIPTION OF THE INVENTION This invention will now be described by way of example with reference to specific workings thereof in relation to pressure sensitive copying systems of the type in which a colourless, chromogenic material of basic reactant chemical properties held in solution in an oily solvent in micro-capsules is reacted, upon rupturing of the micro-capsules by an applied pressure, with a coreactant material, such as attapulgite clay, acid treated montmorillonite clay, or particles of an oil-soluble, acidic, phenolic, polymeric material, to provide distinctive coloured marks. The micro-capsules can be carried on one surface of a transfer sheet known as a CB sheet, and the co-reactant material carried on one surface of a separate record sheet, known as a CF sheet. Otherwise, the microcapsules and the co-reactant material can be carried together on the same surface of a single sheet.

In the workings of the present invention hereinafter described the capsules used had walls of gelatin and gum arabic enclosing an internal phase comprising the dye substances crystal violet lactone and benzoyl leuco methylene blue dissolved in a solvent including dibenzylbenzynes (as described in United Kingdom Patent Application Nos. 44474/71 and 2785/72, now cognated), and diluted with kerosene. However, many different kinds of capsules are known which could otherwise be used.

Five samples of milled wheatflour (bakers soft flour) were made up into aqueous suspensions as indicated in the following table, the procedure being as follows.

Water with a standard defoaming agent added was preheated to the required temperature (see below).

The required weight of wheatflour was added to the preheated water while being stirred.

Caustic soda (when used) was added as a 5N solution.

This method of preparation is necessary since if the water is not pre-heated, i.e. it is heated after addition Sample Water Temp. Stir Timc Caustic Soda added No. "C min. w/w

l 22C 60 0 2 22C 60 0.5 3 50C l0 0.5 4 50C 20 0 5 50C 20 0.5

The five suspensions were then made up into 17% solids coating mixes by admixture with a dispersion of the described capsules at a parts by weight ratio of capsules to 30 wheatflour.

The coating mixes were then coated onto a 49 g/m base paper, using a pilot plant coating machine, with a coating weight of 7 g/m to give CB paper as described.

The CB papers thus produced were then subjected to three tests, namely l a test to measure the distinctiveness of the mark produced by the paper on a standard CF paper; (2) a test to measure the resistance of the CB paper to accidental rupture of the capsules thereon; and (3) a test to measure the adhesion of the capsules and starch particles of the CB paper to the base paper thereof.

All of the samples tested were found to be satisfactory from a commercial point of view.

Instead of wheat flour, one can use flour of Indian com (maize), potato, sweet potato, sago, tapioca, rice, glutinous rice, glutinous corn or arrowroot.

I claim:

1. A process for producing a capsule-carrying sheet or web comprising a base sheet or web having on a surface thereof a coating comprising capsules, protective particles as protection for the capsules, and a binder for the capsules and the protective particles, wherein the protective particles are starch particles and the binder is a protein binder with the starch particles and the protein binder being both derived from a common milled flour source, which process comprises (a) treating milled flour to provide the starch particles and the protein binder, and (b) coating the starch particles and protein binder onto the base sheet or web together with the capsules.

2. The process of claim 1 wherein the milled flour is treated by agitation of an aqueous suspension thereof.

3. The process of claim 1 wherein the milled flour is treated to remove small size range starch particles prior to treatment thereof to derive the starch particles and protein binder.

4. The process of claim I wherein a majority of the starch particles are of a size between about 1 /2 and 2 times the average size of the capsules.

5. The process of claim 1 wherein said starch particles and said protein binder are derived from a flour selected from the group comprising flours of wheat, Indian corn, potato, sweet potato, sago, tapico, rice, glutinous rice, glutinous corn and arrowroot.

6. The process of claim 1 wherein the capsules have walls of gelatin and gum arabic.

7. The process of claim 1 wherein the capsules contant chemical properties held in solution in an oily soltain the dye substances crystal violet lactone and benzoyl leuco methylene blue.

8. The process of claim 1 wherein the capsules contain a colourless, chromogenic material of basic reac- 5 vent.

9. The product of the process of claim 1. 

1. A PROCESS FOR PRODUCING A CAPSULE-CARRYING SHEET OR WEB COMPRISING A BASE SHEET OR WEB HAVING ON A SURFACE THEREOF A COATING COMPRISING CAPSULES, PROTECTIVE PARTICLES AS PROTECTION FOR THE CAPSULES, AND A BINDER FOR THE CAPSULES AND THE PROTECTIVE PARTICLES, WHEREIN THE PROTECTIVE PARTICLES ARE STARCH PARTICLES AND THE BINDER IS A PROTEIN BINDER WITH THE STARCH PARTICLES AND THE PROTEIN BINDER BEING BOTH DERIVED FROM A COMMON MILLED FLOUR SOURCE, WHICH PROCESS COMPRISES (A) TREATING MILLED FLOUR TO PROVIDE THE STARCH PARTICLES AND THE PROTEIN BINDER, AND (B) COATING THE STARCH PARTICLES AND PROTEIN BINDER ONTO THE BASE SHEET OR WEB TOGETHER WITH THE CAPSULES.
 2. The process of claim 1 wherein the milled flour is treated by agitation of an aqueous suspension thereof.
 3. The process of claim 1 wherein the milled flour is treated to remove small size range starch particles prior to treatment thereof to derive the starch particles and protein binder.
 4. The process of claim 1 wherein a majority of the starch particles are of a size between about 1 1/2 and 2 times the average size of the capsules.
 5. The process of claim 1 wherein said starch particles and said protein binder are derived from a flour selected from the group comprising flours of wheat, Indian corn, potato, sweet potato, sago, tapico, rice, glutinous rice, glutinous corn and arrowroot.
 6. The process of claim 1 wherein the capsules have walls of gelatin and gum arabic.
 7. The process of claim 1 wherein the capsules contain the dye substances crystal violet lactone and benzoyl leuco methylene blue.
 8. The process of claim 1 wherein the capsules contain a colourless, chromogenic material of basic reactant chemical properties held in solution in an oily solvent.
 9. The product of the process of claim
 1. 